In the processing and use of multifilament yarns textured with such devices, the mutual cohesion of filaments plays a substantial role. Yarns with good internal cohesion are not only easier to process but they also have a higher wear resistance in use. Thus a high serviceability of the yarns results, e.g, as sewing yarns or the textile fabrics produced with the yarns. The internal cohesion of the textured multifilament yarns is often also designated as the entanglement level.
Additionally, the textured multifilament yarns have the property that filaments project from a yarn core part and are formed in loops. The shape and distribution of the loops projecting from the yarn core part are important for the appearance and textile feel of the fabrics. Although the shape and distribution of the loops are greatly determined by the type of the fed yarns and the settings (pressure of the blowing medium and yarn feed and removal rate in or out of the texturing device), the jet-bulking device also makes a substantial contribution. A good texturing device should have the ability to distribute the loops uniformly and to lay them closely on the yarn core part.
The distribution of the filaments in the yarn bundle is also important, for example, it is responsible for the uniformity of the color component distribution in yarns, which are produced from feed yarns with filaments of different colors or with differently dyed filaments. Such yarns are typically used for the production of seat covers. Bunching individual color components greatly spoils the effect in the finished product.
It is expected of an effectively working jet-bulking device that it produce a uniform, compact texture even at a high yarn excess delivery. The yarn excess delivery is defined as the ratio of yarn feed rate into the texturing device to the removal rate, and is calculated separately for each yarn strand fed to the nozzle. Typically, for highly excess-delivered yarns at least two multifilament yarns or strands are fed, namely a core yarn or stayer yarn with an excess delivery of 1.03 to 1.2 and at least one effect yarn strand with an excess delivery of 1.2 to 4.